Pressure exchangers



y 1963 D. B. SPALDING 3,091,083

PRESSURE EXCHANGERS Filed Nov. 16, 196i United States Patent Office 3,091,083 Patented May 28, 1963 3,091,083 PRESSURE EXCHANGERS Dudley Brian Spalding, 2 Vineyard Hill Road, London, England Filed Nov. 16, 1961, Ser. No. 152,891 2 Claims. (Cl. 6039.45)

This invention relates to pressure exchangers.

At certain stages during the operating cycle of a pressure exchanger, fiuids of different properties are simultaneously present in a cell. For example, at the highpressure scavenging stage of a gas-generating pressure exchanger without transfer passages, hot ga enters cells containing compressed air. Because the whole of each cell end is not instantaneously opened to the port of the inlet duct, a jet of hot gas enters along the leading wall of the cell and an oblique interface is established. Turbulence due to the velocity difference between the compressed air in the cells and the jet of hot gas entering the cells inevitably causes mixing of the cell contents at least in an intermediate zone between the newly introduced hot gas and the original cell contents.

The simultaneous presence of contiguous fluids of differing density also introduces a tendency towards mixing when compression and expansion waves pass through the length of the cells in appropriate directions. The diiferent densities cause the interface to become unstable when a compression wave moves in the opposite sense. An unstable interface results in mixing because of turbulence inevitably present. Mixing may also be experienced as the result of centrifugal forces caused by rotation of the cell wheel. The centrifugal acceleration may be capable of reduction to zero at the designed operating condition for one stage of operation, eg by use of cell walls inclined to the rotor axis, but the effect is necessarily present at other stages and can only be counteracted to some extent by circumferential sub-division of cells and by increasing rotor diameter without increasing cell height.

The pressure exchanger according to the present invention is concerned with the problem of mixing due to tur bulence in the cells, which creates an unstable interface between the compressed air in the cell and the jet of hot gas entering the cells. An object of the invention is to improve the efficiency of the pressure exchanger by reducing the rate of turbulent mixing in the cells and creating a more stable interface.

An embodiment of the invention will now be described by way of example only with reference to the accompanying diagrammatic drawing, which shows a peripheral development of a pressure exchanger gas producer.

The drawing shows a pressure exchanger cell ring I mounted for rotation between end-plate structures 2 and 3, each adjacent opposite ends of the cells. The direction of relative rotation between the cell ring 1 and the end-plate structures 2 and 3 is indicated by an arrow 4.

A low pressure scavenging stage includes an inlet duct 5, which communicates with a first entry port 6 in the end-plate structure 3 and an outlet duct 7, which cornmunicates with a first extraction port 8 in the end-plate structure 2. The first entry port 6 has opening and closing edges 9 and 10 respectively having regard to the direction of relative rotation between the cell ring 1 and the end-plate structures 2 and 3. The first extraction port 8 has opening and closing edges 11 and 12 respectively.

A high-pressure scavenging stage includes an inlet duct 13, an outlet duct 14, an interconnecting duct between the inlet and outlet ducts 13 and 14 and an off-take duct 16 for the removal of compressed air from the outlet duct 14. A flame tube 17 is located in the inlet duct 13 in communication with the interconnecting duct 15 and offset in this duct to form a passage 18 bypassing the flame tube 17. The interconnecting duct 15 is of larger crosssection than the by-pass passage 18. Fuel is supplied to the flame tube 17 via a pipe 19. At the end of the flame tube 17 adjacent the cell ring, a wall 20 constitutes a land which divides the end of the inlet duct 13 adjacent the cell ring 1 into two ports, a second entry port 22 and an additional entry port 21. The opening and closing edges of the second entry port 22 are shown as edges 23 and 24, the opening edge 23 of the port being formed by one edge of the wall 20 of the flame tube 17. The opening edge of the additional entry port 21 is shown as an edge 25 and the closing edge 26 of this port is formed by the other edge of the wall 20 of the flame tube 17. The outlet duct 14 of the high-pressure scavenging stage communicates with a port 27 in the end-plate structure 3 and is referred to as the second extraction port 27. The second extraction port 27 has opening and closing edges 28 and 29 respectively. The sequence of the ports in the endplate structure 2 commencing from the low-pressure scavenging stage is as follows: (i) first extraction port 8; (2) additional entry port 21; and (3) second entry port 22. The sequence of the ports in the end-plate structure 3 commencing from the low-pressure scavenging stage is the first entry port 6 and the second extraction port 27. Commencing from the lowpressure scavenging stage, the sequence of the opening and closing edges of the ports having regard to the direction of relative rotation and considering the end-plate structures 2 and 3 together, is as follows: (1) opening edge 11; (2) opening edge 9; (3) closing edge 12; (4) closing edge 10; (5) opening edge 25; (6) opening edge 28; (7) closing edge 26; (8) opening edge 23; (9) closing edge 24; and (10} closing edge 29.

The operation of the pressure exchanger gas-generator according to the invention will now be described.

Consider a particular cell A of the cell ring I initially at a position X prior to its communication with the first entry and extraction ports 6 and 8. The cell contains gas which entered the cells at the high-pressure scavenging stage as will subsequently be explained. The gas in the cell A in the position X has a pressure slightly higher than atmospheric pressure. As the cell A having regard to the direction of cell rotation indicated by the arrow 4, passes the opening edge 11 of the first extraction port 8, the gas commences to discharge from the cell A and produces an expansion wave as shown in broken line at 30. The pressure inside the cell is reduced by this expansion process and, as a result, fresh air passes into the cell A as soon as its leading wall passes the opening edge 9 of the first entry port 6. The admission of fresh air into the cell creates a compression wave as shown in full line at 31. The effect of the compression wave 31 is to raise the pressure of the contents of the cell A. The cell A is now assumed to be in a position denoted by the reference Y and contains fresh air. The leading wall of the cell A passes the opening edge 25 of the additional entry port 21, which is in communication with the bypass passage 18. Since the interconnecting duct 15 is of larger cross-section than the by-pass passage 18, the stagnation pressure in the interconnecting duct 15 is higher than the stagnation pressure in the by-pass passage 18. Consequently, air, which is compressed by a process which will be subsequently explained, enters the cell A via the additional entry port 21 and creates a compression wave 32 as shown in full line. The compression wave 32 commences at the opening edge 25 of the additional entry port 21 and travels to the opening edge 28 of the second extraction port 27. The location of the additional entry port 21 is such that the compression wave 32 initiated at the opening edge 25 of this port passes through a cell and reaches the opposite end of this cell when this end of the cell communicates with the leading portion of the second extraction port 27.

The cell A, on passing the land formed by the edges 26 and 23 of the wall 20 of the flame tube 17, comes into communication with the second entry port 22. The cell is then in communication with the main high-pressure scavenging stage. High-pressure gases leaving the flame tube 17 enter the cell A via the second entry port 22 and create a further compression wave 33 commencing at the opening edge 23 of the second entry port 22 and travelling towards the second extraction port 27. As these highpressure gases enter the cell A, the cell contents have already been put in motion by the compressed gas entering the cell via the additional entry port 21. The air contained in the cell A is compressed by the entering high-pressure gases and the thus compressed air is discharged from the cell via the second extraction port 27. The compressed air is recirculated via the interconnecting duct 15 and a part of the air flows through the bypass passage 18 and enters a cell via the additional entry port 21 to create the compression wave 32 previously referred to. The leading portion of the second extraction port 27 and the bypass passage 18 operate as a subsidiary high-pressure scavenging stage. The interconnecting duct 15 is common to both the main and subsidiary high-pressure scavenging stages. The compressed air, apart from that passing through the bypass passage 18 and any quantity extracted through the duct 16, re-enters the cells via flame tube 17 as combustion gases. As the cell A leaves the closing edge 24 of the second entry port 22, an expansion wave 34 is created travelling from the closing edge 24 of the second entry port 22 towards the closing edge 29 of the second extraction port 27. The pressure of the cell contents falls, owing to this expansion, to a pressure slightly higher than atmospheric pressure by the time the cell returns to the position X. The cycle of low and highpressure scavenging for the cell A is now complete and it will be understood that each of the cells of the cell ring 1 following the cell A pass through the same cycle.

The compressed air entering the cell A via the bypass passage 18 and the additional entry port 21 is heated by passing over the flame tube 17 and forms a jet of warmed compressed air as the leading edge of the cell passes the opening edge of the additional entry port 21. The properties of this jet are much more nearly equal to those of the compressed air in a cell in the position Y, that is approaching the high-pressure scavenging stage, than they are to the hot gas (combustion products) which is subsequently going to pass into the cells from the flame tube 17 via the second entry port 22. Mixing is thus avoided between hot compressed gas (combustion products) entering the cells from the second entry port 22 and the air, substantially at rest, as contained in the cell A in the position Y. Two interfaces 35 and 36 indicated by chain lines are established within the cells, thereby substantially separating the hot gas entering the cells via the second entry port 22 from the cool gas already in the cells coming from the low-pressure scavenging stage, for example as contained by the cell A at the position Y. The interface 35 lies between the initial contents of the cell A at the position Y and the compressed air entering through the additional entry port 21. The second interface 36 lies between the air entering the additional entry port 21 and the gas entering through the second entry port 22. Thus, between the interfaces 35 and 36, a butler zone is established, the air in this zone leaving the cells of the pressure exchanger via the second extraction port 27. It will be understood that the recirculation of compressed air for the formation of a buffer zone has no first order effect on the pressure exchanger performance, although slightly increased pressure losses can be expected because of the additional duct surface area. It will be noted that the buffer zone of compressed air between the interfaces 35 and 36 is not carried through the complete cycle of operation, but only through the high-pressure scavenging stage.

The mixing which occurs between the air entering through the additional entry port 21 and the gas entering through the second entry port 22 is reduced further in importance by ensuring that the air entering through the additional entry port 21 is travelling at a somewhat higher velocity than that of the hot gas entering through the second entry port 22. This arrangement results in a retardation effect in the vicinity of the gas-to-air interface, any irregularities therein being minimised as a result.

I claim:

1. A pressure exchanger comprising in combination:

(a) a ring of cells,

(2)) an end-plate structure adjacent each end of the cells,

(0) the end-plate structures having located therein first and second entry and extraction ports,

(d) means to effect relative rotation between the cell ring and the end-plate structures,

(e) the second entry and extraction ports operating at a higher pressure than the first entry and extraction ports,

(1) ducting to lead fluid to the cells via said entry ports and from the cells via said extraction ports.

(g) the end-plate structure adjacent one end of the cell ring having an additional entry port,

(h) the additional entry port being located adjacent the second entry port and separated by a land from the opening edge of this port,

(i) interconnecting ducting between the additional entry and the second extraction ports,

(j) the second extraction port being so located with respect to the additional entry port that a compression wave initiated at the opening edge of this port passes through a cell and reaches the opposite end of this cell when this end of the cell communicates with the leading portion of the second extraction port, and,

(k) the additional entry port, part of the extraction port and said interconnecting ducting being operable as a subsidiary higher pressure scavenging stage to extract fluid from the cells before the composition of the fluid has been affected by the fluid passing through the second entry port and to introduce said extracted fluid into the additional entry port, said fluid having properties which are more nearly equal to the properties of the initial contents of the cells before they reach the additional and second entry ports having regard to the direction of relative rotation, than to the fluid subsequently entering the cells of the pressure exchanger via the second entry port, but at a pressure substantially equal to the pressure of the fluid in the second entry port.

2. A pressure exchanger as claimed in claim 1, in which there is:

(a) a flo-w connection upstream of the additional entry port between the interconnecting ducting and the ducting leading fluid to the second entry port, and

(b) a flame tube,

(0) said flame tube being incorporated in the ducting leading fluid to the second entry port,

(d) the part of the interconnecting ducting downstream of the flow connection by-passing the flame tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,848,871 Jendrassik Aug. 26, 1958 2,852,915 Jendrassik Sept. 23, 1958 2,970,745 Berchtold Feb. 7, 1961 

1. A PRESSURE EXCHANGER COMPRISING IN COMBINATION: (A) A RING OF CELLS, (B) AN END-PLATE STRUCTURE ADJACENT EACH END OF THE CELLS, (C) THE END-PLATE STRUCTURES HAVING LOCATED THEREIN FIRST AND SECOND ENTRY AND EXTRACTION PORTS, (D) MEANS TO EFFECT RELATIVE ROTATION BETWEEN THE CELL RING AND THE END-PLATE STRUCTURES, (E) THE SECOND ENTRY AND EXTRACTION PORTS OPERATING AT A HIGHER PRESSURE THAN THE FIRST ENTRY AND EXTRACTION PORTS, (F) DUCTING TO LEAD FLUID TO THE CELLS VIA SAID ENTRY PORTS AND FROM THE CELLS VIA SAID EXTRACTION PORTS. (G) THE END-PLATE STRUCTURE ADJACENT ONE END OF THE CELL RING HAVING AN ADDITIONAL ENTRY PORT, (H) THE ADDITIONAL ENTRY PORT BEING LOCATED ADJACENT THE SECOND ENTRY PORT AND SEPARATED BY A LAND FROM THE OPENING EDGE OF THIS PORT, (I) INTERCONNECTING DUCTING BETWEEN THE ADDITIONAL ENTRY AND THE SECOND EXTRACTION PORTS, (J) THE SECOND EXTRACTION PORT BEING SO LOCATED WITH RESPECT TO THE ADDITIONAL ENTRY PORT THAT A COMPRESSION WAVE INITIATED AT THE OPENING EDGE OF THIS PORT PASSES THROUGH A CELL AND REACHES THE OPPOSITE END OF THIS CELL WHEN THIS END OF THE CELL COMMUNICATES WITH THE LEADING PORTION OF THE SECOND EXTRACTION PORT, AND, (K) THE ADDITIONAL ENTRY PORT, PART OF THE EXTRACTION PORT AND SAID INTERCONNECTING DUCTING BEING OPERABLE AS A SUBSIDIARY HIGHER PRESSURE SCAVENGING STAGE TO EXTRACT FLUID FROM THE CELLS BEFORE THE COMPOSITION OF THE FLUID HAS BEEN AFFECTED BY THE FLUID PASSING THROUGH THE SECOND ENTRY PORT AND TO INTRODUCE SAID EXTRACTED FLUID INTO THE ADDITIONAL ENTRY PORT, SAID FLUID HAVING PROPERTIES WHICH ARE MORE NEARLY EQUAL TO THE PROPERTIES OF THE INITIAL CONTENTS OF THE CELLS BEFORE THEY REACH THE ADDITIONAL AND SECOND ENTRY PORTS HAVING REGARD TO THE DIRECTION OF RELATIVE ROTATION, THAN TO THE FLUID SUBSEQUENTLY ENTERING THE CELLS OF THE PRESSURE EXCHANGER VIA THE SECOND ENTRY PORT, BUT AT A PRESSURE SUBSTANTIALLY EQUAL TO THE PRESSURE OF THE FLUID IN THE SECOND ENTRY PORT. 